1. Field of the Invention
The present invention relates to touch panels. More particularly, the present invention relates to a touch panel integrated with liquid crystal display device driven according to a line inversion method.
2. Discussion of the Related Art
Touch panels have been developed as a means of efficiently interfacing with electronic devices via a display surface. For example, users may input desired information using a touch panel integrated with a display device while watching images displayed by the display device. Allowing users to easily input desired information to an electronic device via a display surface, touch panels substantially reduce or eliminate the need for other types of input devices (e.g., keyboards, mice, remote controllers, and the like) that tend to have higher rates of malfunction the touch panels replacing them. Currently, touch panels have been widely used as input devices integrated with, or added to, electronic devices such as computers, portable information devices, personal digital assistants (PDAs), and spherical or non-spherical display devices (e.g., liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescence (EL) devices, cathode ray tubes (CRTs), etc.).
Depending on the type of contact object used (e.g., a user's finger, a stylus, etc.), and on the manner in which the location of a contact point (i.e., the location where the contact object is operably proximate the touch panel) is determined, touch panels are generally classifiable as analog resistive-type, digital resistive-type, capacitive-type, ultrasonic wave-type, and infrared-type touch panels.
Generally, analog resistive-type touch panels include an upper transparent substrate supporting an upper electrode and a lower transparent substrate supporting a lower electrode. The upper and lower transparent substrates are attached to each other and spaced apart from each other by a predetermined distance. When a surface of the upper transparent substrate is contacted by a contact object, the upper electrode formed on the upper transparent substrate electrically contacts the lower electrode formed on the lower transparent substrate. When the upper and lower electrodes electrically contact each other, a voltage, made variable by a resistance value or a capacitance value specific to the location of where the user touched the touch panel (i.e., the contact point), is then detected and outputted along with a location defined by coordinates of the contact point.
FIG. 1 illustrates a cross-sectional view of a related art touch panel integrated with an LCD device.
Referring to FIG. 1, the related art touch panel generally includes a lower polarizing plate 110, a lower substrate 120 of an LCD panel 100 provided on the lower polarizing plate 110, an upper substrate 130 of the LCD panel 100 provided over the lower substrate 120 of the LCD panel 100, an upper polarizing plate 140 provided on the upper substrate 130, a lower substrate 210 of a touch panel 200 provided on the upper polarizing plate 140, and an upper substrate 220 of the touch panel 200 provided over the lower substrate 210 of the touch panel 200. A case top 300 is provided at a side of the structure described above and arranged over a periphery of the touch panel 200. Generally, the upper substrate 130 and the lower substrate 120 include a color filter array (not shown) and a thin film transistor array (not shown), respectively. Further, a liquid crystal layer (not shown) is provided between the substrates 120 and 130.
FIG. 2 illustrates a plane view of the related art touch panel 200 shown in FIG. 1. FIG. 3 illustrates a cross-sectional view taken along line I-I′ of FIG. 2.
Referring to FIG. 2, the related art touch panel 200 generally includes a viewing area (VA) having dimensions corresponding to a display surface of an LCD device and a dead space region (DS) formed to surround the periphery of the viewing area (VA).
Referring to FIG. 3, the upper and lower substrates 220 and 210 are each formed of a PET (polyethylene terephtalate) film and are adhered together via an insulating glue 230 arranged within the dead space region (DS). The insulating glue 230 is provided to a predetermined thickness for spacing the upper and lower substrate 220 and 210 apart to a predetermined thickness. Transparent electrodes 221 and 211 are provided on opposing inner surfaces of the upper and lower substrates 220 and 210, respectively, and have dimensions corresponding to dimensions of the viewing area (VA). A signal line 240 connects to one of the upper and lower transparent electrodes 221 and 211 within the dead space region (DS) and extends outside the touch panel 200. Accordingly, the signal line 240 transmits a voltage to one of the transparent electrodes 221 and 211 and receives a voltage made variable based on the location of the contact point. A plurality of dot spacers 250, formed of an insulative synthetic resin (e.g., epoxy or acrylic acid resin), are uniformly arranged on the lower transparent electrode 221 to prevent the upper and lower transparent electrodes 221 and 211 from electrically contacting each other in the presence of inadvertent or otherwise insufficient contact pressure.
During operation of the resistive-type touch panel, the transparent electrodes 221 and 211 electrically contact each other at a contact point when a contact object (e.g., a pen, a finger, etc.) touches a predetermined location (i.e., a contact point) of the upper substrate 220 with a pressure equal to an operating pressure. Accordingly, a voltage, made variable by a resistance value specific to the contact point, is outputted through the signal line 240. However, when the contact area touches the upper substrate 220 with a pressure less than an operating force, the dot spacers 250 prevent the upper and lower transparent electrodes 221 and 211 from electrically contacting each other.
FIG. 4 illustrates a cross-sectional view of the LCD panel 100 shown in FIG. 1.
Referring to FIG. 4, the LCD panel 100 typically includes upper and lower substrates 130 and 120 attached to, and spaced apart from, each other and a liquid crystal layer 150 provided between the upper and lower substrates 130 and 120.
The upper substrate 130 includes a shielding layer 131 for preventing light from being transmitted from the LCD panel in areas outside pixel regions, a color filter layer 132 for enabling red (R), green (G), and blue (B) colors to be displayed, a common electrode 133 for enabling pictures to be displayed.
The lower substrate 120 includes a plurality of gate lines (not shown), a plurality of data lines (not shown) crossing the plurality of gate lines, a plurality of pixel regions arranged in a matrix pattern defined by crossings of the gate and data lines, a plurality of pixel electrodes provided in the plurality of pixel regions, and a plurality of thin film transistors (TFTs) connected to corresponding ones of the gate lines, data lines, and pixel electrodes, for switching data signals, generated by a data driver (not shown) and applied to data line, to a pixel electrode in the presence of a signal applied to a gate line.
Generally, each TFT includes a gate electrode 121 provided on the lower substrate 120, a gate insulating film 122 provided over the lower substrate and on the gate electrode 121, a semiconductor layer 123 provided on the gate insulating film 122 over the gate electrode 121, and source/drain electrodes 124a and 124b provided at opposing sides of the semiconductor layer 123. A protective layer 125 is provided over the lower substrate 120 and on the semiconductor layer 123 and source/drain electrodes 24a and 24b. A pixel electrode 126 is provided on the protective layer 125 and is electrically connected to the drain electrode 24b. 
The upper and lower substrates 130 and 120 are uniformly spaced apart from each other by spacers (not shown) and are bonded to each other via seal material (not shown). The seal material includes a hole that facilitates the injection of liquid crystal 150 between the bonded upper and lower substrates 130 and 120.
During operation, the aforementioned related art LCD applies picture signals to pixel electrodes connected to corresponding TFTs in receipt of scanning signals are applied from a gate line. When the picture signals are applied to the pixel electrodes, an electric field is generated between the pixel electrode and the common electrode 133. Subsequently, the orientation of molecules within the liquid crystal 150 become altered in the presence of the generated electric field. Upon altering the orientation of the liquid crystal molecules, pictures are thus displayed. However, the liquid crystal material 150 can become damaged if it is exposed to a DC electric field for an excessive amount of time. Accordingly, the polarity of the generated electric field is changed periodically during driving of the LCD device to prevent the liquid crystal from becoming damaged, wherein the polarity of the generated electric field corresponds to the polarity of data signal voltages applied from data lines to the pixel electrodes.
Such driving is referred to as polarity inversion driving and includes frame inversion (wherein the polarity of the electric field is inverted every frame period), line inversion (wherein the polarity of the electric field is inverted for every horizontal line of pixel regions), column inversion (wherein the polarity of the electric field is inverted for every vertical line of pixel regions), and dot inversion (wherein the polarity of the electric field is inverted both for every horizontal line and vertical line of pixel regions).
Driving LCD devices using the line inversion driving method, and by providing an AC voltage to the common electrode 133, reduces the degree to which the LCD flickers as compared with the frame inversion driving method and requires less power than the dot inversion driving method. Accordingly, LCD devices are commonly driven according to the line inversion method.
FIG. 5 illustrates a method by which an LCD device is driven according to the line inversion method.
Referring to FIG. 5, and as mentioned above, when LCD devices are driven according to a line inversion method, the polarity of the generated electric field is inverted for every horizontal line of pixel electrodes, wherein the polarity of the electric field within each pixel region is inverted between successive frame periods (e.g., n and n+1). For example, during the nth period, electric fields having a positive polarity are generated within odd numbered horizontal lines of pixel regions and electric fields having a negative polarity are generated within even numbered horizontal lines of pixel regions. During the (n+1)th period, electric fields having a negative polarity are generated within odd numbered horizontal lines of pixel regions and electric fields having a positive polarity are generated within even numbered horizontal lines of pixel regions. Accordingly, the polarity of data signal voltages applied to pixel electrodes within adjacent horizontal lines are opposite each other.
By driving LCD devices according to the line inversion method, a brightness deviation between horizontal lines is smaller than the frame inversion methods. Due to spatial averaging, LCD devices driven according to the line inversion method flicker less than those driven according to the frame inversion method. Moreover, the opposite polarity voltages are vertically distributed through the LCD device. As a result, coupling phenomena generated between data signal voltages are offset and vertical cross talk is reduced compared to the frame inversion method.
FIGS. 6a and 6b illustrate output waveforms of data drivers used to drive LCD devices according to dot inversion and line inversion methods, respectively.
Referring to FIGS. 6a and 6b, compared to the output range of data signals outputted in a dot inversion method (as shown in FIG. 6a), the output range of data signals outputted in a line inversion method (as shown in FIG. 6b) can be reduced because the polarity of the voltage applied to the common electrode can be inverted in correspondence with the polarity of data signal voltages applied to the horizontal line being driven. More specifically, in driving LCD devices according to the line inversion method, the polarity of the common voltage is made to be opposite the polarity of the pixel signal voltage.
Aside from the aforementioned benefits obtained from driving LCD devices according to the line inversion method, problematic generation of horizontal cross talk is generated using the line inversion method. Moreover, as the switching frequency increases between each frame, the power consumption of the LCD device increases. Further, when the related art touch panel, having the lower transparent electrode 211, is integrated with the aforementioned related art LCD device, driven according to the line inversion method, a parasitic capacitor is undesirably formed.
More specifically, first and second electrodes of the parasitic capacitor include the common electrode 133 of the LCD device 100 and the lower transparent conductive film 211 of the touch panel 200, respectively, separated by an interposing dielectric structure that includes the upper polarizing plate 140 and the upper substrate 130. Accordingly, the AC signals applied to the common electrode 133 in applying the line inversion method, undesirably interfere with and distort voltages applied to, and transmitted from, the touch panel 200.
For example, where the touch panel 200 is provided as the aforementioned resistive-type touch panel described above with respect to FIG. 3, voltages indicative of the location of the contact point are applied to the lower transparent conductive film. However, due to the electromagnetic interference generated by the AC signal applied to the common electrode 133, the exact location of the contact point generated on the touch panel 200 is impossible to be determined detect a contact area on the touch panel.
Where, however, a capacitive-type touch panel having a glass reinforcing film laminated to a transparent conductive film is integrated with the LCD device 100, a parasitic capacitance is generated between the common electrode 133 and the transparent conductive film. Similar to the manner in which the AC signal applied to the common electrode 133 interferes with signals of the resistive-type touch panel, the AC signal applied to the common electrode 133 electromagnetically interferes with voltage signals transmitted by metal electrodes provided at corners of the transparent conductive film used to form an equipotential field and to detect the location of the contact point.
Moreover, where an electromagnetic (EM)-type touch panel, having a sensor board and an electronic pen, is integrated with the LCD device 100, the AC signal applied to the common electrode 133 electromagnetically interferes with the detection of a generated contact point. More specifically, the sensor board of the EM-type touch panel is provided at a rear surface of the LCD for generating electromagnetic fields and a control board for detecting the location of generated contact points based upon the interaction of the electronic pen and the generated electromagnetic field. Accordingly, the AC signal applied to the common electrode 133 interferes with the interaction between the generated electromagnetic field and the electronic pen.